Antifungal activity of ethanolic extract of Archu (Rheum emodi) on powdery mildew (Erysiphe cichoracearum) and its role in the induction of resistance in balsam (Impatiens balsamania)

Rheum emodi, vernacularly known as Archu, is one of the important high altitude medicinal plants widely distributed in Himalayan regions. Though widely used in Ayurveda for curing various human diseases, its use in plant diseases is limited. Ethanolic extract of Rheum rhizome was assayed against spore germination of Alternaria solani, Heliminthosporium penniseti and Curvularia palliscens. The inhibition of spore germination was concentration dependent. Maximum inhibition was obtained at 4000 and 5000 ppm followed by 3000, 2000 and 1000 ppm. However, the extract was highly effective in the pre-inoculation treatment against powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsamania) under field conditions. High performance liquid chromatographic (HPLC) analysis of balsam leaves showed increased synthesis of phenolic acids, which has been correlated with induced resistance in inhibiting the disease intensity of balsam powdery mildew.